1. Field of the Invention
The present invention relates to a linear motor for use in various industrial machinery, such as, e.g., electrical component mounting apparatuses, semiconductor related apparatuses, or machine tools, and suitably used for driving the direct acting mechanism thereof, and more specifically to a moving magnet type linear slider equipped with a magnetic field system having permanent magnets as a moving unit and an armature having an armature winding as a stator.
2. Description of Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
FIGS. 6A and 6B show a conventionally available moving magnet type linear slider for use in various industrial machinery, such as, e.g., electrical component mounting apparatuses, semiconductor related apparatuses, or machine tools, and suitably used for driving the direct acting mechanism thereof. FIG. 6A is a plan view of a conventional moving magnet type linear slider, and FIG. 6B is a cross-sectional view taken along the line B-B in FIG. 6A.
In FIGS. 6A and 6B, the reference numeral “21” denotes a fixed base, “22” denotes a magnet track, “23” denotes a field permanent magnet, “24” denotes a field yoke, “25” denotes a guide rail, “26” denotes a guide block, “27” denotes a sensor head, “28” denotes a linear scale, “29” denotes a stopper, “30” denotes an armature, “31” denotes an armature coil, and “32” denotes a circuit board.
In the linear slider shown in FIGS. 6A and 6B, the field yoke 24 is provided on the back of the field permanent magnet 23. The field yoke 24 serves as a movable unit and a magnetic circuit. The armature 30 is provided with a plurality of slotless armature coils 31 fixed to a circuit board 32 arranged on the fixed base 21 made of solid magnetic material so as to face the movable unit via a magnetic gap, which constitutes a stator. A plurality of hall elements (not illustrated) for performing magnetic pole detection are embedded in the circuit board 32 so as to face the field permanent magnet 23. The hall element (not illustrated) detects the position of the field magnet opposed to the hall element at the time of the early stage when the electric power supply is turned on, and outputs a detection signal for passing a driving current through the armature coil 31 in response to the position of the detected field magnet 23 (see, for example, Japanese Unexamined Laid-open Patent Publication No. H09-266659, page 5 of the specification, FIG. 3).
At both sides of this armature 30, guide rails 25 and 25 arranged in parallel are fixed on the fixed base 21, and guide blocks 26 and 26 slidably disposed on the guide rails 25 and 25 are fixed to the lower surfaces of both end portions of the field yoke 24. At the side of the movable unit, a magnetic type linear scale 28 constituting a linear type encoder is provided. A sensor head 27 for detecting the linear scale 28 is provided at the fixed base 21 so as to face the linear scale 28. Stoppers 29 and 29 each for preventing the overrun of the movable unit are provided between the end portions of the two guide rails 25 and 25.
This linear slider has a magnetic circuit structure in which the magnetic flux of the field permanent magnet 23 interlinks the fixed base 21, and is configured such that the movable unit is linearly moved within a stroke which is a difference between the length of the armature 30 and the length of the movable unit by the shifting magnetic fields formed by the field 23 and the armature 30 when the armature coil 31 is excited (see, for example, Japanese Unexamined Laid-open Patent Publication No. H09-266659, page 5 of the specification, FIG. 3, and Japanese Unexamined Laid-open Patent Publication No. H2002-10617, pages 7-9 of the specification, FIGS. 1 and 3).
In the conventional linear slider, since it is configured such that the armature 30 and the field permanent magnet 23 constituting the linear motor face with each other at each one side, a magnetic suction force will act between these two members. Therefore, the linear motor is supported by the guide rails 25 and 25 and the guide blocks 26 and 26 arranged in two rows to reduce the torsion moment caused by the magnetic suction force. This structure, however, increases the guide friction caused by the magnetic suction force acting on the linear guide. Furthermore, parallelism errors of the guide rails 25 and 25 cause partial friction changes in the stroke direction, resulting in inconstant thrust, which in turn prevents minute thrust control.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.